The typical JS heap is above 90MB out of the box. Locker service is the main culprit for that, and Locker Service does cause some slowdown. Server-side, they ar

The typical JS heap is above 90MB out of the box. Locker service is the main culprit for that, and Locker Service does cause some slowdown. Server-side, they are multitenant and the tenants you are sharing compute with are frequently running massive data operations on a regular basis. Those tenants have no incentive to get things running faster because they don't pay for compute hours. As long as the operations run within Salesforce's governor limits, who cares? Salesforce's response to the client-side half of the problem is migrating from Aura to Lightning Web Components. LWC is statically analyzable and Aura is not, so they can get some optimizations in that way. On the flip-side, LWC is a piss-poor framework because of how they've stunted it for optimization's sake. Half of the beauty of Salesforce as a developer is the fact that I can build in a month what would typically take a standard web dev team a year to piece together. That's only true so long as my team works in Aura with all of the scaffolding tools and libraries we've built over the years.